Mac Pro 3,1, PCIe SSD operating at only 2.5GT/sec

Long time no post :slight_smile:

I picked up a Mac Pro 3,1 pretty cheap and chucked in a Samsung SM951 PCIe SSD, sitting in a Lycom DT-120 M.2 PCIe SSD to PCIe 3.0 x4 adapter (both purchased from RamCity, heh). It works well and boots fine, but the transfer speed is limited to only around 700MB/sec.

Looking in system profiler shows me that whilst it’s got 4x PCIe lanes, it’s only operating at 2.5GT/sec, which would explain why benchmarking the SSD using Blackmagic’s app only results in a max of 700MB/sec.

This leads me to believe it’s in PCIe 1.0 mode for some reason. The Lycom DT-120 is supposed to be good at this, it supports PCI 3.0 and 2.0. Dunno why the Mac Pro 3,1 has decided to operate it in PCIe 1.0 mode. The SSD is in Slot 2 (next to the graphics card - which is operating happily in 16x 5GT/sec mode), which is supposed to have full 16x PCIe 2.0 speeds, regardless of what’s plugged in to slot 1. Or am I wrong?

The only thing I can think of trying it another adapter off eBay (this one), but is there something else I’m missing here?

Have you tried it in another of the PCIe slots?

Not sure if the 2008 will be the same as the 4,1 and 5,1 that Barefeats tested, but I do recall that when they put an SM951 in slot 2 of their 2010 Mac Pro it only negotiated 2.5GT/s.

When they stuck it in slot 3 or 4 then it ran at 5.0GT/s.

Taken directly from here.
http://barefeats.com/hard200.html

  1. If you are installing it in the PCIe bay of your 2009-2012 Mac Pro tower, you must use slot 3 or 4 to get the transfer rates we reported. If you install it in slot 2, it will work but the link speed drops from 5.0GT/s to 2.5GT/s resulting in a maximum transfer speed of 786MB/s.

Yeah, just chucked it into slot 3 and slot 4 and the same issue - which I expected, as slot 3 and 4 are PCIe 1.1 slots.

Seems like it’s an issue with the SM951 SSD, someone on MacRumors had the same issue. It fails to auto negotiate the link speed as it’s expecting PCIe 3.0 (which the Mac Pro doesn’t have). This doesn’t appear to be an issue on the 4,1+ Mac Pros :frowning:

It’s still plenty fast and better than SATA-2 included on the machine, but damn it’d be nice to have the proper link speed. Wish there was a way to force it to 5GT/sec somehow.

I was also considering a similar upgrade to my 3.1 MacPro but you get to a point of diminishing improvements for a 2008 machine.

I vaguely remember following the a macrumors forum, on the best combination of ssd and pci adaptor. I think at one stage, the advice was that the best results were with a SSD pulled from a 15"MBP. Although that might have been more to do with TRIM before el capitan.

Eventually bought a late 2015 iMac, links at 8GT/s, max transfer just under 1900MB/s. listing my 3.1 for sale in the trading forum

iMacs are so expensive if I want an SSD in it :frowning:
Brand new I’d be looking at $2019 for the base level iMac with a 256GB SSD. Not cool.

Yes they are,but I paid about $3300 in 2008 for a macpro with 2GB of RAM and a 1TB spinning HD and no display

The Mac Pro has had a great RoI. I had one back in the day too - should have kept it :frowning:
I don’t think any of the Macs these days will hold their usefulness like the 2008 Mac Pro did.

Yeah, I’m still using mine and it’s very usable with an SSD and a decent graphics card. The only thing that really pisses me off about these machines is power management - mine uses 150-200 watts at idle, 35 watts asleep and about 30 watts when it’s off. That’s ridiculous.

That kind of power consumption is pretty normal for high-end/workstation class boxes, but I’m questioning the power usage when off — that seems very strange.

You’re welcome to question it but I made all those measurements myself. :slight_smile: It’s crappy power management. I had a G5 tower too, which have a terrible reputation for power consumption, but it was better than the Pro. Mine’s only single processor too. It’s not a problem where it is now because it runs off a hybrid solar system, so the power costs me nothing in effect, but 30W when off is a fail. Even in 2008 for this class of machine.

But off? If so I’ll have to be buying a wattmeter — my current one only measures draw when the PC is on.

It’s expected that there will be some power consumption because if you can start your computer from a button on a keyboard, there needs to be a bit of stuff running to power the USB bus and interpret a key press. The new Macs are all much better and my Minis use less than 5W off and not much more asleep. That’s very good performance I reckon and something the Pros should have been closer to. I don’t know if the later models were the same or not, but I think the 1,1 (2006) was also very power hungry.

Hi there. I am glad I found this thread. Just installed the SM951 with the Lycom-adapter, also in the good old Mac Pro 3.1 on 10.10.5.
Unfortunately it´s not recognised by my mac. Any hints would be highly appreciated. :slight_smile:
Cheers, and thanks in advance.

4 posts were split to a new topic: Where is the private message option?

decryption, if there´s any chance to get in contact with you I´d appreciate that a lot. I´d like to get the same set-up as the one you have. I did search quite a lot in the net and you seem the be the man able to help me. If you´re busy it´d be no problem though. We all have lots of things to do. :slight_smile:

my mail: putte at gmx dot com

Cheers!

Paging @decryption

I tried to email you, but the email bounced :frowning:

Looks like you’ve having an issue with the SM951?

I don’t know what you’ve done, but have you tried booting off a USB drive with the Mac OS X installer on it and running disk utility? You need to format the drive before the installer will see it.

Thanks again Erwin, and of course decryption for the fast response. Well appreciated. :slight_smile:

The thing is that the drive isn´t recognized in Disk Utility. It is recognized in the “about this mac”-window under PCI.
I guess I bought the wrong SM951. Mine is the MZ-VPV2560 and I learned that there are different versions of the SM951.

@recd I’m loving the Mac Pro. :wink: Put a decent video card in, 4x 3.5-inch HDDs and an 1TB 850 Pro SSD. Awesome machine. :smiley:

@decryption I just stuck a Samsung 850 Pro in the optical bay (ran a SATA cable from the board up). How much faster does it feel in your setup than a standard SATA SSD?